Method for continuous supersonic inspection of hot steel plates

ABSTRACT

IN DETECTING FLAWS IN STEEL PLATES AT A RELATIVE HIGH TEMPERATURE BY ULTRASONIC SIGNALS, A STEEL MATERIAL OF THE SAME QUALITY AS A STEEL PLATE TO BE TESTED IS EMPLOYED AS AN ACOUSTIC COUPLING, THE STEEL MATERIAL IS FORMED INTO A CYLINDRICAL ROLLER IN ORDER TO PERFORM CONTINUOUS AND AUTOMATIC INSPECTION, AND A HIGH PRESSURE WITHIN THE NONDESTRUCTIVE RANGE IS APPLIED TO THE STEEL MATERIAL TO REALIZE AN EXCELLENT ACOUSTIC COUPLING. THEN THE STEEL MATERIAL IS HEATED TO PREVENT GENERATION OF AN ABRUPT HEAT TRANSFER IMPACE.

(s e-yaw raw M QR maze-11.051 ARCH-ROOM METHOD FOR uuu'uuuOUS SUPERSONICINSPECTION 0F HOT STEEL PLATES Filedsept. 25, 1969 5 Sheets-Sheet 1 MATLFOR l- JMHW M W l TRANSDUCER FOR RECEIVING PRE COOL'NG W (NOR TEMP) 70CW-TIGHT 535 dB TRANSDUCER Qm/fl 1 50- z m Z SI TO BE HEATED INVENTORSuiekiy- LJozumi ATTORNEYS.

Dec. 7, 1971 SUTEKIYO UOZUMI 3,525,051

METHOD FOR CONTINUOUS SUPERSONIC INSPECTION OF HOT STEEL PLATES FiledSept. 25, 1969 Sheets-Sheet 2 F 3 TRANSDUCER Bl 1 F 6 l'rz a m le sa 64b86 a 4 3 o s02 (kg/(m 1 PRESS. AT CONT SUR 2o- TRANSDUCER +F FIG. 4

, F I as 1 g 5 C com DEPTH L "lm i zooiss'zo i $0 i I530 3000 4590 eloo'nF 6 PRESS. AT com SUR 'NVENTOR Sutekiw Uozumi BY We! fl'x e ATTORNEYS.

Dec. 7, 1971 SUTEKIYO UOZUMI 3,525,051

METHOD FOR CONTINUOUS SUPERSONIC INSPECTION OF HOT STEEL PLATES FiledSept. 25, 1969 5 Sheets-Sheet 3 WT|GHT F TRANSDUCE F I G. 5 l I HEATINGMATL" A l 4 PRESS.2TON F 6 0-8 TON izi'sifol lfz MATL TEMP moovc)INVENTOR Sutekiyo Uozumi BYWf/ ATTORNEKS,

1971 SUTEKIYO uozuw 3,625,051

METHOD FOR CONTINUOUS SUPERSONIC INSPECTION OF HOT STEEL PLATES FiledSept. 25, 1969 5 Sheets-Sheet 4 INVENTOR Sufekiyo ldzumi BY w ATTORNEYS,

Dam 7. 9'7 SUTEKIYO UOZUMI 3,625,051

METHOD FOR CONTINUOUS SUPERSONIC INSPECTION OF HOT STEEL PLATES 5Sheets-Sheet 5 Filed Sept. 25, 1969 FIG.?

INVENTOR Uozumi Sutekiyo ATTORNI Y3.

3,625,051 METHOD FOR CONTINUOUS SUPERSONIC INSPECTION OF HOT STEELPLATES Sutekiyo Uozumi, Tokyo, Japan, assignor to Electronics ResearchCo. Ltd, Kanagawa, Japan Filed Sept. 25, 1969, Ser. No. 870,374 Claimspriority, application Japan, Get. 1, 1963, 43/ 70,789 int. Cl. Gtlln29/00 US. Cl, 737L5 5 Claims ABSTRACT OF THE DISCLUSURE In detectingflaws in steel plates at a relative high temperature by ultrasonicsignals, a steel material of the same quality as a steel plate to betested is employed as an acoustic coupling, the steel material is formedinto a cylindrical roller in order to perform continuous and automaticinspection, and a high pressure within the nondestructive range isapplied to the steel material to realize an excellent acoustic coupling.Then the steel material is heated to prevent generation of an abruptheat transfer impact.

BACKGROUND OF THE INVENTION The present invention relates to a methodfor the continuous and automatic inspection of steel plates which are ata relative high temperature condition by means of ultrasonic, orsupersonic, waves or pulse. The object of the invention is to provide anovel supersonic flaw detecting method which overcomes the limitationsand other difficulties encountered in conducting the conventionalmethods for relative high temperature and high speed inspection whichhave been attempted hitherto, in order to make it possible to etfect thecontinuous flaw detection of steel plates over an extremely wide scopeof temperature, ranging between normal temperature and the level ofabout 1,200 C. This capability has long been demanded by the steelmanufacturing industry.

In a known supersonic inspecting method, a jet, or stream, of water isutilized for attaining acoustic coupling. Basically the fundamentalprinciple of the water stream jet method resides in acoustic coupling byuse of a liquid. In other words, it is intended to achieve acoustic wavepropagation between a liquid phase and a solid phase, eliminating thepresence of any gaseous phase medium. However, as temperature of thesteel plate being tested is raised over a certain level, the conductionof heat from the steel plate to the water stream is sharply promoted,and a water-gasifying area is produced close to the testing steelsurface. As a result, a mingled area of gas phase and liquid phase whichis most undesirable for acoustic coupling would be produced, and thisinvited generation of abnormal noises made it impossible to detect flawsin a steel plate at a temperature over said range. Further, the case ofusing a water jet as an acoustic coupling means, there is producedanother difiiculty which cannot be physically overcome in achieving theprimary object in liquid phase contact; the critical temperature andcritical pressure of water are 374.1 C. and 218.5 atmospheres pressure(a.p.) respectively, and its density under these conditions is 0.324gr./cm. (See International Critical Table or Chronological Table ofPhysico-Chemistry 1968, Material 68.) in other words, theoreticallyspeaking, unless the temperature of the steam layer produced at theboundary face between the water and a hot steel surface is kept below374.1 C. it is impossible to eliminate the gaseous layer and produce aninterfacial condition desirable for acoustic coupling; i.e. where waterof liquid phase and steel of solid phase would be contacted with eachother. no matter. how

easiest Patented Dec. Y, 191 1 much the pressure is increased. Hereexists the fundamental temperature limitation for supersonic inspectionby means of a water stream jet. Therefore, in order to inspect steelplates having a higher temperature than this limitation by this method,it is required to reduce the temperature of the inspecting area of thesteel surface below said limitation temporarily, at least during tneinspecting operation, through a pre-cooling means.

On the other hand in order to suppress the generation of the steam phaseat the interface, it is required to provide a pressure of more than 1a.p. at C., more than 4.698 a.p. at C., more than 15.34 a.p. at 200 morethan 39.23 a.p. at 250 C., and more than 163.2 a.p. at 350 C. (SeeChronological Table of Physico- Chemistry 1968, Material 69), so that itis extremely difficult to realize an ideal interfacial contactedcondition between liquid phase and solid phase at a relative hightemperature area by using a water stream. Therefore, supersonicinspection has conventionally been conducted under the presence of asteam layer having a sufiiciently small thickness when compared with thelength of the supersonic waves used. Moreover both the unstable v-ariation in thickness of this steam layer produced by a relative high speedfeeding of steel plate and the sudden heat transfer transient impactappearing the moment the water jet impinges on the hot steel surface areconsidered. as the primary factors which cause the generation of theabnormal noise signal witnessed in the inspecting operation for therelative high temperature steel plate by the conventional method. (SeeStudy Report on Automatic Supersonic Inspection for Thick Plates, pages133l34 and page 143,. published by the Learning and Study AdvancementSociety of Japan.)

There is, additionally, great difiiculty in the practical aspect;namely, the attempt to raise up higher the pretended upper limit of thetemperature range where inspec tion is conducted by using pre-coolingresults in producing a great deal of steam, since more cooling waterimpinges on the surface of a steel plate having a huge heat capacity,and the steam then hangs over the testing field and causes excessiverusting of the steel plate.

As set out above, the conventional method using a water jet isaccompanied with several difficulties which make it quite impossible toperform supersonic inspection under the condition of high temperaturei.e. ranging up to about 1,200 C. Indeed, there is reported an examplewhere steel inspection was successfully achieved in and at a temperaturein which salt is molten by using molten salt instead of water as anacoustic coupling means. However, the use of molten salt as an acousticcoupling means for continuous and automatic inspection has never beenpractised partly due to economical disadvantage and partly due todifliculty in the removing operation of said salt.

SUMMARY OF THE INVENTION It is a desired object of the present inventionto surmount such limitations and difficulties as observed in theconventional methods and provide a novel method for continuousinspection under a wide range of temperature, i.e. between normaltemperature and 1,200 O, which has long been awaited by the steelmanufacturers.

This object is achieved according to the present inven tion by using asthe acoustical coupling a steel material of the same quality as thesteel plate being tested. Either echo pulse or through transmissionultrasonic pulse systems may be used, and the steel material may be incontact with one surface or a pair of opposing surfaces of the plate being inspected.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side viewillustrating a representa tive example of the conventional hot steelplate inspection 3 system wherein a water stream is utilized as anacoustic coupling means.

FIG. 2 is a graph showing a plot of supersonic wave attenuation with thegrowth of temperature gradient in a steel material.

FIG. 3 is the graph showing a plot of fiaw detection sensibility versuspressure at normal temperature in planeto-plane contact.

FIG. 4 is the graph showing a plot of flaw detection sensibility Versuspressure at normal temperature in cylindrical face-to-plane contact.

FIG. 5 is the graph showing a plot of flaw detection sensibility as afunction of the testing materials temperature in cylindricalface-to-plane contact with and under pressure.

FIG. 6 is a front elevation view of an example of a practical deviceemployed in applying the present invention.

FIG. 7 is a side elevation view of the device of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 of the drawings showsschematically an example of a prior art ultrasonic inspecting system. InFIGS. .l, 2 and 5, W is used to designate water; and. in FIG. 1 Rdesignates rollers.

FIGS. 2 to 5' show graphs which were made under the condition that thegraduation of the vertical axis (dB) was the value indicated at theattenuator when the amplitude of the echo pattern which is of the bottomor of an artificial flaw of 6 0 fiat bottomed on a cathode ray tube wasa constant value of, for example, 50 mm.

The curves B1 and F1 shown in FIG. 3 and FIG. 4 denote respectively backecho character and flaw echo character.

Referring first to FIG. 2, it should be noted that the primary factorwhich has made flaw detection of relative hot steel plates byultransonic, or supersonic signals impossible is not the temperaturedependency of the supersonic wave attenuation in the steel material, butthe unsuitability of the acoustic coupling means. As shown by the graphin FIG. 2, it was confirmed that any supersonic wave attenuation largeenough to make flaw detection impossible is not produced even if thereexists a heavy temperature gradient ranging between the normaltemperature of C. and the high temperature of 1,200 C., where the steelmaterial becomes clear orange-colored in a identical steel material.

It has thus become evident that the problem resides in the method foracoustic coupling of the interface S where the supersonic wave comes inand out. The present inventor has solved this problem in the followingmanner based on the next two facts; one is that, in general, the optimumcondition for penetrating a supersonic wave from medium A to medium E isobtained when acoustic impedances, i.e. the density x times the soundspeed, of both media are equal. The other is, the above-mentioned factthat the variation of supersonic wave attenuation is within only few dBat most, even if such a heavy tempera ture gradient as that between1,200 C. and 30 C. should exist in the identical steel material. Basedon these two facts, the inventor has attained the idea of using a steel:as a material which is inserted between the transducer and the surfaceof testing steel plate to form a temperature gradient, hereinafterreferred to it as temperature gradient delay line material, and stronglypressing both steel ma terials toward each other with a force F so as toremove the interfacial gas phase and thereby achieve excellent acousticcoupling. The practicability of the idea is demonstrated by the graphshown in FIG. 3 which is based on an experiment.

Then, for conducting continuous inspection, the configuration of thetemperature gradient delay line material is shaped into the form ofhollow cylindrical roller so as to roll on in contact with a material tobe tested. More over a high pressure is applied to the contacting facesto remove the interfacial gas phase and realize an excellent acousticcoupling. However, it is a basic rule that the high pressure is withinthe non-destructive range, so as not to produce any injuriousdeformation or deterioration of the quality of the material to betested. For composing a supersonic wave transferring system between thestation ary part of the roller, in which the transducer and the movablepart of the roller, some suitable means may be employed; for example, acooling oil may be circulated through said hollow cylindrical roller,and an oil tight transducer placed on a pedestal and mounted to thecentral fixed shaft of the roller. The central fixed shaft has a leafoil film between said pedestal and the inner face of said roller, andthe pedestal serves as both the temperature delay line material 2mg Iconcentrates supersonic beams on the surface el plate being tested. Theefiiciency of the means for continuous inspection mentioned above isconfirmed by the graph shown in FIG. 4 which is also based on anexperiment.

In addition, as a measure to arrest an abnormal transient signal whichis likely to be produced at the moment of contact between the acousticcoupling material and the hot steel plate being tested in the case ofrelative high-speed and temperature inspection, an arrangement is madesuch as to prevent generation of abrupt heat transfcrring impact fromsaid steel plate toward the roller of the temperature gradient delayline material at the moment of contact. Namely, this problem can besolved by approximating the surface temperature of said roller to theone of said testing steel plate. According to this method, the noiseproduced at the contact moment, as shown in FIG. 5, is so small that itmay hardly be perceived.

An example of the mechanical composition of the device used in applyingthe present invention is embodied as shown in FIG. 6 and FIG. 7, wherein1 denotes a steel plate to be tested, 2 a chain coupling, 3 a tableroller, 4- a water introducing part, 5 an oil pressure cylinder, 6 awater discharging part and high frequency cable, 7 a cylindrical roller(housing a transducer therein), 8 a bearing, 9 take-up units (only oneof which is shown) and 10 a heating burner. Axial length l of thecylindrical roller 7 may be suitably selected as the circumstances demand. For example, when it is desired to attainuniformity of theinspection, an elongated cylinder arranged such as to cover the entirewidth of steel plate 1, shown in FIG. 6, may be formed by a suitablemeans, e.g. by using suit able back-up roller 11. In such a case asusing an elongated cylindrical roller, multi transducers may be arrangedin the roller as the number of channels demanded.

As understood from the foregoing description and the accompanyingdrawings, the present invention is an effective one providing acontinuous supersonic inspecting method for hot steel plates whosetemperature may range between normal temperature and 1,200 C.

It should be understood that the above described supersonic inspectingmethod for steel plates may be used not only for a single transducersystem wherein signal trans mission and reception are effected by thesame transducer on one side of the testing steel plate according to apulse echo, but for a two-transducer system wherein signal transmissionand reception are respectively effected by a different transducer, orfor a signal penetration system wherein signal (pulse wave or continuouswave) transmitting and receiving transducers are respectively providedat both sides of the testing steel plate. FIG. 6 and FIG. 7 show adevice employing the pulse echo system.

As various changes might be made of the above device used in applyingthe present invention, it is to be understood that all matter herein setforth or shown in the accompanying drawings, is to be interpreted asillustrative and not in a limiting sense.

What I claim is:

1. In a method for the continuous ultrasonic flaw 1nspection of steelplates having a surface wherein ultrasonic signals are transmitted intoand received from a plate to be tested through an acoustical coupling,the improvement comprising the step of utilizing an element, of the sagequality steel as the plate, as the acoustical coupling by put-= 6 actionof the hollow cylindrical roller and at least one table.

5. The method of claim 1, the improvement further including the step ofapplying pressure to the steel element tirig'it in contact with thesurface of the plate, and the step 5 and the steel plate by means of afluid cylinder, so as to of heating the element with a suitable heaterprior to putting it in contact with the surface of the plate so as toprevent generation of abrupt heat transfer impact by approxi mating inthe element the temperature of the plate,

2., The method of claim 1 wherein the ultrasonic signals are transmittedand received by a single transducer,

3 The method of claim 1 wherein the ultrasonic signals are transmittedby a first transducer and received by a sec ond transducer 4. The methodof claim 1, the improvement further in-= 15 cluding the steps of shapingthe s t eel element lingo the for? of a hollow cylindrical roller, witha centra Ye'dhli'iiti circulating mingmrough the hollow roller, placingan oil-tightgap sd u ceron a pedestal mounted to the central, fixedshaft,.oflthe 611 leaf oil'fil m between the pedestal "and the innerface of the hollow roller and serving as both a preceding temperaturedelay line material and a lens which concentrates ultra sonic beams ontothe surface of the steel plate to be tested, which plate is beingadvanced continuously by combined press the element and plate togetherand eliminate the inter facial gas phase between them, the pressure usedbeing within the non-destructive range of the material so as not toproduce any injurious deformation or deterioration of 10 the quality ofthe plate being tested.

References Cited UNITED STATES PATENTS 3,531,982 10/1970 Clutfelter etal. 73-71.5 X 3,548,644 12/1970 OConnor et al. 7371'.,5 3,242,723 3/1966Evans at, 73-=-7L5 3,404,551 10/1968 Spisak 73-675 X 3,423,993 1/1969Lynnworth 73- 715 611% the Pedestal having a 20 RICHARD (J, QUEISSER,Primary Examiner A. E. KORKOSZ, Assistant Examiner US. (:1. X.R,

